This invention relates to flip-chip type semiconductor devices sealed with cured products of epoxy resin compositions of inorganic filler loading type affording the cured products having low stress and high transparency.
While the recent advance of the information technology requires effective transmission and processing of a vast quantity of information bits, what is now under investigation as a substitute for conventional signal transmission through electrical wiring is semiconductor devices which take advantage of the high speed, low loss, non-induction and other desirable features of optical signals and mounting technology used therefor. In particular, interest has increased in applications where ultra-high speed, ultra-high density and ultra-low loss are required as in flip-chip type central processing units (CPU).
Most of prior art opto-functional devices are sealed with epoxy resins which are free of inorganic filler in order that the resin layer be transparent. Such unfilled epoxy resins are not satisfactory when the heat resistance, humidity resistance and low stress property of cured parts are taken into account. On the other hand, conventional epoxy resin compositions for semiconductor encapsulation are loaded with finely divided silica as the inorganic filler. Cured products of such filled compositions have good heat resistance, moisture resistance and low stress property, but are opaque because of the difference in refractive index between the cured epoxy resin and the inorganic filler.
U.S. Pat. No. 5,175,199 discloses a light transmission epoxy resin composition comprising
(A) a curable epoxy resin,
(B) a curing agent, and
(C) silica-titania glass beads having a linear transmittance of at least 70% as measured at a wavelength in the range of from 900 nm to 600 nm by a linear transmittance measurement method, said method comprising
mixing a bisphenol type epoxy resin of the general formula (1) shown below or a novolak type epoxy resin of the general formula (2) shown below with phenylglycidyl ether to form a solution having a difference in refractive index from the silica-titania glass beads within xc2x10.002,
mixing the solution with the silica-titania glass beads which have been ground to a mean particle diameter of 5 to 30 xcexcm in a weight ratio of 1:1, and
measuring the linear transmittance of the mixture across a light path length of 1 mm,
wherein formula (1) is 
xe2x80x83where n is an integer of from 0 to 10, and formula (2) is 
xe2x80x83where n is an integer of from 0 to 10.
However, the epoxy resin composition of U.S. Pat. No. 5,175,199 is not so sufficient for the use requiring a low stress as in the case of encapsulating a flip-chip type semiconductor device.
There is a need for an epoxy resin sealant which is transparent despite filler loading and has a lower stress.
An object of the invention is to provide a flip-chip type semiconductor device sealed with a cured product of a light-transmissive epoxy resin composition of inorganic filler loading type which exhibits high transparency and imparts a lower stress in the cured state.
It has been found that when an epoxy resin composition comprises an epoxy resin of the following general formula (i), a curing accelerator, and an amorphous silica-titania co-melt as an inorganic filler as essential components and satisfies the relationship of the following formula (1), cured products thereof become highly transparent despite the presence of inorganic fillers and impart an improved low stress, thereby providing a flip-chip type semiconductor device for optical communications sealed with the cured product of the epoxy resin compositions.
Accordingly, the invention provides a flip-chip type semiconductor device sealed with a light transmissive epoxy resin composition comprising
(A) an epoxy resin having the following general formula (i): 
xe2x80x83wherein n is 0 or a positive number,
(B) a curing accelerator, and
(C) an amorphous silica-titania co-melt as at least one of inorganic fillers,
said composition satisfying the relationship of the following formula (1):                                           [                                          {                                                      2                    ⁢                                          (                                                                        n                          A                          2                                                +                                                  n                          C                          2                                                                    )                                                        -                                                            (                                                                        n                          A                                                +                                                  n                          C                                                                    )                                        2                                                  }                            /              2                        ]                                1            /            2                           less than                   3.0          xc3x97                      10                          -              3                                                          (        1        )            
xe2x80x83wherein nA is the refractive index at 25xc2x0 C. of the cured product of the composition excluding the inorganic fillers, and nC is the refractive index at 25xc2x0 C. of the inorganic fillers.